The invention relates to a suspension system for an inner container mounted for thermal insulation in an outer container.
Furthermore, the invention relates to an arrangement of an outer container and of an inner container mounted for thermal insulation in the outer container.
From Document EP 0 014 250 A1, a suspension system for a cryogenic tank is known, by means of which the cryogenic tank is suspended in an outer container in a thermally insulated manner. The suspension system comprises several securing straps, each composed of several series-connected single elements of different fibre materials, wherein the single element of each securing strap which is closest to the tank is made up of the fibre material having the comparatively lowest thermal expansion coefficient. The securing straps are able to absorb only tensile forces, but no compression forces. Therefore, it is necessary to group the securing straps to two fixed bearings engaging opposite end regions of the cryogenic tank, with the tensile forces of the two fixed bearings acting in opposite directions. A fixed bearing results only from the sum of all securing elements. A prerequisite for this is a geometric arrangement of the securing elements which compensates for the thermal length changes of the respective containers and of the securing straps themselves as far as possible, since, otherwise, the thermal tensions would burden the device up to the admissible load limit.
From DE 196 25 492 C1, a toroidal cryotank filled with liquid helium is known, which, via a suspension system, is suspended coaxially in a cylindrical outer container aboard a research satellite. The suspension system consists of an upper and a lower rectangular frame, each composed of tension and pressure bars in the manner of a framework, and tie rods running under prestress obliquely between the respective corner points of the rectangular frames and the outer container. Thus, the cryotank is connected to the outer container only via the tie rods. The tie rods are able to absorb only tensile forces, but no compression forces.
From Document U.S. Pat. No. 3,115,983, a suspension system for a multi-walled cryogenic spherical liquid storage tank is known. The outer container rests on pillars extending vertically upwards from a base. The outer container is connected to the inner container by means of a plurality of loop-shaped tension members 15. The tension members are distributed around the inner diameter of the outer container and extend in the space between the outer container and the inner container. On the one hand, the tension members are fixed with their two ends to support base members 14 located in pairs on the inside of the outer container and, on the other hand, enlace curved lateral edges of pad plates 17 attached to the outer wall of the inner container. Because of the enlacement, the pad plates are supported in the tension members as a result of gravity. In order to prevent the tension members from gliding off the curved lateral edges of the pad plates 17, retaining lugs 18 are provided, which, however, do not clamp the tension members. Since only gravity acts upon the inner container, the tension members are only stressed in tension and may therefore be constructed as ropes, cables or chains. It is also mentioned that the tension members may be designed as appropriately shaped rigid rods, but also in such an embodiment, the tension members will not absorb any compression forces, since, with a force acting upwards onto the inner container, the pad plates would lift off from the tension members. With forces acting laterally upon the inner container, the rod-shaped tension members would slip out of place along the semi-circular edges of the pad plates. As is mentioned in the document, such movements are desirable for the compensation of thermal tensions. From a mechanical point of view, the mounting of the inner container on the outer container thus constitutes a floating bearing.
As is generally known, in mechanics, a distinction is made between floating bearings and fixed bearings. A fixed bearing transmits forces acting in space in all directions. With a floating bearing, no connection exists in one or two of the three directions in space, and a force transmission in said direction is thus impossible. Thus, a floating bearing permits a movement of the mounted body in at least one spatial direction.
Document DE 103 45 958 A1 discloses a tank for cryogenic liquids which is intended for installation in motor vehicles and consists of an outer container and an inner container suspended therein in tension or compression struts. The spatially arranged tension or compression struts compensate for displacements of the inner container as a result of differences in thermal expansion. In order to optimally meet the opposing requirements in motor vehicles, stoppers and supporting surfaces are additionally provided between the outer container and the inner container, which can be brought to a distance in a stationary vehicle and into contact in a moving vehicle. The stoppers in the interior of the outer container co-operate with supporting surfaces at the inner container and are displaceable by means of an actuator. In a stationary vehicle, the stoppers do not abut on the supporting surfaces. The inner container is then connected to the outer container only by means of the tension or compression struts, which is regarded as sufficient, since shaking normally does not occur if the motor vehicle is at a standstill. Thus, the tension or compression struts can be designed so as to be very light-weight and with a very small cross-section so that they will form only minimal thermal bridges. For the vehicle operation, the stopper is switched into contact with the supporting surface. The inner container is now free from play and firmly connected to the outer container, the inner container is thus fixed in the outer container, and the tension or compression struts are unloaded. Hence, a fixed bearing of the inner container at the outer container is formed only if the stopper is switched into contact with the supporting surface. The struts absorb either tensile forces or compression forces and, as a result of their small cross-sections, are unsuitable for supporting the inner tank during vehicle operation.
Document DD 281 319 A7 discloses a bearing for double-walled containers of cryogenic media and is usable equally for stationary tanks and for transport containers for road and rail transport. The bearing is composed of at least three rings or ring segments, the ends of which are interconnected in the shape of a meander. Depending on whether an asymmetric or a symmetric structure of the meander has been chosen, a ring or, respectively, the outer rings thereof is/are attached to the outer container and a ring or, respectively, the central ring thereof is loosely connected to the inner container. Said bearing permits the transmission of large radial forces, but does not absorb any noteworthy axial forces. Hence, this is a floating bearing with axial freedom of motion for compensating for thermal length changes of the inner container. Two floating bearings of this type keep the inner container therewith in a radial direction. For axial safeguarding, one of the two floating bearings must be axially supported by an additional measure, for which the inclusion of a cone is recommended. A fixed bearing results only from the combination of the radial mounting with the axial support.
Document DD 281 318 A7 discloses a bearing for double-walled containers of cryogenic media and is usable equally for stationary tanks and for transport containers for road and rail transport. The bearing is configured as a meander-shaped hollow profile supporting, in its longitudinal axis, a central flange which is connected to the inner container, whereas, by contrast, the outer end of the hollow profile is fastened to the outer container. A single bearing element—consisting of a meander-shaped hollow profile with a central flange—constitutes a floating bearing. Since it is not fixedly connected to the inner container in order to avoid thermal tensions, it constitutes, strictly speaking, a floating bearing which can be stressed only in compression. A fixed bearing in a technical sense is achieved only by several bearings offset from each other in spatial directions. The bearings are arranged in an annular installation space between the inner container and the outer container, which is referred to as an annular gap.
There is still a need for a highly stable and rigid suspension system for an inner container mounted for thermal insulation in an outer container. Even if high dynamic forces act upon the outer container and the inner container as well as the suspension system, as they occur, for example, with the application in vehicles or in case of shocks, the stability and the rigidity of the suspension system must be maintained and forces must be introduced into the containers in a distributed fashion, without high local force peaks. It is in particular an object of the invention to develop a suspension system by means of which a mounting of an inner container in an outer container in a thermally insulated manner is feasible, which is highly rigid and very capable of bearing, without or with comparatively minor specific stiffening measures at the containers. It is also an object of the invention to provide a suspension system and a container arrangement provided therewith which are inexpensive to produce and easy to assemble.